Electrical musical instrument



@ct 259 1949. N. LANGER ELECTRICAL MUSICAL INSTRUMENT 4 Sheets-Sheet 1 Filed Oct. 27, 1945 4 Sheets-Sheet 2 N. LANGER ELECTRICAL MUSICAL INSTRUMENT oct. 25, 1949.

Filed OC'C. 27, 19,45

N. LANGER 2,486,039

4 Sheets-Sheet 3 ELECTRICAL MUSICAL INSTRUMENT Oct. 25, 1949.

Filed oct. 27, 1945 Oct. 25, 1949.

N. LANGER ELECTRICAL MUSICAL INSTRUMENT Filed Oct. 27, 1945 4 Sheets-Sheet 4 Mdo/a5 Zalig am. www

Patented Oct. 25, 1949 ELECTRICAL MUSICAL INSTRUMENT Nicholas Langer, New York, N. Y., assgnor to Central Commercial Company, Chicago, Ill., a

corporation of Illinois Application October 27, 1945, Serial No. 625,018

12 Claims. l

The present invention relates to electrical musical instruments, and', more particularly, to electrical musical instruments of the type Wherein the electrical oscillations to be converted into musical sound are produced by means of space discharge devices. The most common forms of such space discharge devices are the conventional electron tubes which comprise a sealed envelope having a, pluralityof electrodes arranged therein, for example acathode. a plate and one or more auxiliary or control electrodes, the said envelope being evacuated to an extremely low pressure` or being filled with a suitable gas at a predetermined pressure.

As those skilled in the art know, in practical electrical musical instruments it isfnecessary to make provision for the generation of a large number of oscillations of different frequencies, such oscillations beingv produced in simultaneously present groups in polyphonic or chord instruments and being produced individually and successively in the solo or melodyinstruments. The number of oscillations of different frequencies Which have to be-produced may be quite high in practical instruments, such as up to 87, or more, and in few cases would be less than 61, corresponding to a. chromatic range of octaves. In general, a separate oscillator tube is provided for each one of these frequencies.

One of the principal problems in the design and construction of suchy electrical musical instruments is that of frequency stability. The frequency stability of electron tube oscillation generators is largely a result of judicious design, careful selection of components, and of proper compensation foi` unavoidable variables. Oscillation generators of high frequency stability, however, are bulky and. relatively expansive. Economy of manufacture and of space in the finished instrument make it undesirable to incorporate 60v or 80 of such expensive oscillators intoa single instrument.v Therefore, the recent trend' in the design of such instruments was in the direction of providing only a relatively low number ofexpensive oscillators of high frequency stability and employing each of the said master oscillators to maintain the frequency of several slave oscillators constant. For example, 12 vof such master" oscillators may be providedeach being, tuned to a differentr chromatic note of the highest or the lowest octave within the range of the instrument and each of these master oscillators may be caused to control a plurality of cascaded, octavely related slave oscillators. These slave oscillators may be of a simple and inexpensive construction as their frequency stability does not have to be very high. In most cases, it is suflicient to merely tune the slave oscillators approximately to the desired frequency, the accurate maintenance of such frequency being assured by transferring small amounts of oscillatory energy from the master oscillator to the first slave oscillator, from the first slave oscillator to the second slave oscillator, and soI forth, in` cascade fashion. Electrical musical instruments including such cascaded groups of octavely related master and slave oscillators are disclosed, for example in the Langer Patents 2,044,360; 2,247,728 and 2,252,189.

While harmonically related cascaded oscillators of the described character may be made to operatev quite satisfactorily and commercial instruments based on this principle have been built and sold, such operation is predicated upon critical adjustment of the circuit constants in each oscillator, Subsequent changes in the circuit constants, if small enough, may be initially without effect upon the several oscillators. However, when such changes increase, they will first cause some of the slave oscillators to drop out of their octave relation into some other harmonic relation, such as the fth or the fourth. Further increase ofsaid changes or deviations may cause some of the slave oscillators to assume a non-harmonic relation to the others and thereby to render the instrument inoperative until the proper tuning is restored by manual adjustment.

Experience has also demonstrated that proper operationof such cascadedA systems cannot be obtained or maintained for any' length of time without individual tube selection for the several stages. Replacement of a single tube in a cascaded series with another tube of the same make and type was in general suilicient to throw the entireL series out of synchronism and very small changes in the characteristics of a tube, due to aging, had the same result. As a matter of fact, even mechanical'- shock or vibration, unavoidable during shipment of the instrument, would change the circuit constants to an exfent sufficient to render retuning of the instrument necessary at the place of use. Such retuning would` frequently become necessary even after the instrument has been installed, as a result of changes in tube characteristics, oscillator circuit constants, and other variables.

Another frequently used principle involved the use of cascaded resistance-coupled amplifier stages of special type in combination with master oscillators. The amplifier stages were so adjusted as to cause considerable distortion oi the waveform of the input oscillation of frequency f so that the output would contain a substantial proportion of the harmonics 2f or N2. Under certain conditions, a plurality of such amplifier stages may function as a frequency multiplier or divider system, whereby a series of frequencies harmonically related to each other and to that of the master oscillator may be derived. Although such systems were sometimes referred to as aperiodic frequency changer systems, their operation was by no means truly aperiodic or independent of the frequency, but careful correlation of the time constants of the coupling elements, such as condenser and resistors, to the operating frequencies was absolutely necessary to assure correct operation. Systems of this type likewise depended for their proper operation upon critical adjustment of the circuit constants, as the tubes had to operate within a predetermined narrow range of their characteristics. Therefore, careful tube selection and matching was absolutely necessary, and tube replacements, aging of the tubes and other circuit components had the same detrimental effect upon the tuning of these instruments as upon the instruments employing cascaded series of true oscillators.

The foregoing practical diiiiculties experienced in lobtaining and maintaining the proper tuning of electrical musical instruments have seriously interfered with the manufacture, sale and commercial success of such instruments. Although also various other suggestions and proposals were made to eliminate these difficulties, none, as far as I am aware, of these suggestions and proposals was completely satisfactory and successful when carried out on a practical and commercial scale.

I have discovered a simple and completely satisfactory solution of the outstanding problem.

It is an object lof the present invention to provide an electrical musical instrument which is free from the tuning difficulties heretofore inseparable from the design, construction and operation of such instruments.

It is another object of the invention to provide an electrical musical instrument of novel and improved character comprising truly aperiodic frequency dividing circuits in cascaded arrangement, the `operation of which is completely independent of the input frequency within the frequency range of the instrument.

It is a further object of the invention to provide an electrical musical instrument wherein an oscillation lof stable frequency, obtained from a master oscillator is subjected to repeated frequency-halving operations by means of operiodic trigger circuits of the type generally denoted as flip-nop circuits.

The invention also contemplates a n'ovel system of generating octavely related groups of oscillations including at least one master oscillator capable of producing oscillations 'of a predetermined stable frequency, a series of cascaded stages of scale-of-two electrical counting circuits, whereby the frequency of the master oscillator is successively divided by the factor of two by each stage, and means for selectively withdrawing oscillatory energy of desired octavely related frequencies from one or more of the said stages.

Still another object of the invention is to provide an electrical musical instrument including twelve master oscillators, respectively tuned to the twelve chromatic steps of the tempered scale within the highest octave of the range of the instrument, a plurality of cascaded groups of scaleof-two frequency-dividing circuits, means for selectively connecting said master oscillators to the said groups to cause repeated and progressive frequency-halving of the input frequency, regardless of the value of such input frequency, and means for selectively withdrawing oscillations of the desired frequencies from the corresponding frequency-dividing circuits, for conversion into musical sounds by means of suitable translating devices.

The invention also contemplates an electrical musical instrument which is simple in construction, which is free from critical adjustments, which will retain its correct and proper tuning for very long periods of time, and which may be readily manufactured and sold on a practical and commercial scale at a low cost.

Other and further objects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings; in which Fig. 1 illustrates a circuit diagram of an electrical musical instrument embodying the principles of the `present invention and employing cascaded aperiodic frequency-dividing circuits;

Fig, 2 is a similar circuit arrangement, somewhat diagrammatic in character, of an electrical musical instrument of the melody type embodying the invention;

Fig. 3 is a circuit diagram, similar in character t0 that of Fig. 2, of a modified electrical musical instrument 'of the melody type; and

Fig. 4 is the circuit diagram of a polyphonic electrical musical instrument or organ embodying the principles of the invention.

Referring now more -particularly to the drawings, Fig. 1 illustrates the circuit arrangement of an electrical musical instrument embodying the principles of the present invention and based on the Eccles-Jordan trigger circuit. In this Figure 3 such circuits are connected in cascade fashion and are energized from 3 bus bars of which B-I is connected to a source I0 of positive plate potential of about +150 volts, B-Z is grounded at I l, and B-3 is connected to a source I2 of grid biasing potential of about 100 volts. Of course, in a practical electrical musical instrument a larger number of such cascaded stages is generally employed, such as 6 or '7, in accordance with the desired musical range of the instrument.

The first trigger stage comprises a pair of threeelectrode vacuum tubes T-I and T-2 and two sets fof serially connected resistances, connected between bus bars B-I and B-3. The first of said sets included Rf-I, R-Z and Rf-3, and the other includes lit-4, R-5, R-S and R-l. The grid of tube T-l, is connected to the common point of resistances R2 and R--3, the grid of tube T-2 is connected to the common point of resistances R-S and R-1; the Iplate fof T-2 is connected to the common point of resistances B I and R-Z, and the plate of T I isconnected to the commonpoint of R 5 and R-G. The cathodesi' tubes T I and T 2 are connected to grounded bus bar B 2 through resistances R 8 and R-9, respectively. Condensers C Z and C E are connected across resistances R 2Y and R-S, respectively, and the grids of the two tubes arey connected together by a pair of serially connected condensers C 3 and 0 1. An output pulse may be derived from the stage through a coupling network comprising a cloupling condenser C S and a decoupling resistance R IIJ in series therewith, the said network being arranged between the cathode of tube T 2 and switching key S-I.

The second trigger stage comprises a pair of vacuum triodes T 3 and T 4, operatively 0associated with resistances B I I to R 2Il, andwith condensers C I2, C I3, C I6, C II and C I9. The reference characters employed for the second stage have been derived from those of the rst by adding 10' to the indicia of the corresponding circuit elements. An output pulse may be derived from the second stage through a coupling network comprising a coupling condenser C I9 and a decoupling resistance R-ZI), arranged between the cathode of tube T 4 and switching key S 2.

The third trigger stage comprises a pair of vacuum triodes T 5 and T G, operatively associated with resistances R 2I to Rf-BU, and with condensers C 22, C 23, 0 26, C 21 and C 29. The reference characters employed for the third stage have been derived from those of the rst by adding 20 to the indicia of the corresponding circuit elements. An output pulse may be derived from the third stage through a coupling network comprising a coupling condenser C 29 and a decoupling resistance R-30, arranged between the cathode of tube T B and switching key 8 3.

In view of the fact that stages 2 and v3 are identical in their circuit arrangement with that of stage I, and as similar reference characters have been employed for denoting corresponding parts, as set forth in the foregoing, no detailed description of stages 2 and 3 will be necessary.

The rst stage is coupled to the second by means of a lead wire I3, one end of which is connectedto the common point of resistances R-I and R 5, in the first stage, and the other end of which is connected to the common point of condensers C I 3 and C I'I, inthe second stage. The second stage is coupled to the third by means of a lead wire I4, one end of which is connected to the common point of resistances R I4 and R I5, in the second stage, and the other end of which is connected to the common point of condensers C 23 and C 21, in the third stage. Coupling to a fourth stage, (not shown), may be provided by means of lead wire I5, connected to the common point of resistances Rf-24 and B ZS, in the third stage.

An input pulse of suitable character produced by means of a master pulse generator I6 may be applied to input terminals I1, I8 of the cascaded system of trigger circuits, of which I'I is connected to bus bar B l and I8 is connected to the common point of condensers C 3 and C l, through a condenser C o. A resistance R-o is connected across terminals I'I and I8 and together with condenser C o constitutes a pulsesharpening circuit.

The preferred values of the Various' circuit elements will appear from the following table, it

being understood, however, that the said values are by no means critical and that the desired mode of operation may be obtained by-means of circuit elements having substantially different values.

n l, R n zl 0hms 20,000 n s, R, l4, R 24 do 8,000 n s, n ls, R, 25 do 12,000 R 2,R B,R, I2,R ls,

.Rf-22, 1% 26 do 200,000 R 3,R 1,R |3,R |1,

R 23, R, 21 d0 200,000 R s,R 9,R, |s,R l9,

R 2s, R 29 do 1,000 to 5,000 R |0, R 20, B so d0 10,000 to 50,000 c 2,c 6,o |2,o |s,

o 22, c zs microfarad-- 0.001 C 3,C 1,o |3,c |1,

o zs, c 21 uo 0.0005 c s, c ls, o 29 do 0.0001 to Tubes T I to T may be triodes of any suitable type, preferably having a high transconductance and a comparatively high amplication factor, such as type 6J5. The two triodes employed in each stage may be combined in a single envelope by using twin triodes of the type 6SN7, and the like. This has the advantage of reducing the space requirements of each stage quite considerably.

The output circuit comprises an output bus bar I9 connected to normally open switching keys S I, 5 2, and S 3', and introduces the output pulses derived from the several stages into an amplifier K I, the amplied pulses being converted into sound by means of a translating device L I, such as a loudspeaker of suitable construction.

From the foregoing description, the operation of the electrical musical instrument embodying the invention will be readily understood. Considering the rst stage and initially disregarding cathode resistances R 8 and R-9, the circuit .is reduced to one closely similar to the Eccles-Jordan trigger circuit, sometimes also referred to in the literature as the flip-flop circuit. In a circuit of this type the two triodes T I and T 2 are so interconnected that the plate of each controls the grid of the other and that consequently only one tube can conduct at a time. This will be readily appreciated if it is considered that when, for example, tube T 2 is conducting, there is a substantial potential drop in resistance R so that the grid of T I, connected to the center point of voltage divider network E Z and R 3, will be given a strongly negative bias, maintaining tube T I in the nonconducting state. If now a negative impulse of suitable value is momentarily applied to the grids of both tubes T I and T 2 through input lead wire 20 and input condensers C 3, C 'I, the said impulse will at iirst have no appreciable effect on the grid of T I, which is already biased negative, but will be suicient to instantaneously reduce the grid potential of tube T 2 below cutofl, rendering this tube likewise non-conducting. At the same time, however, in the absence of plate current flow through resistance R I, the potential of the point between resistance R I and R 2 will be rendered strongly positive, and this sudden change in potential instantaneously transferred to the grid of tube T I through condenser C 2 will render the said grid strongly positive and tube T-l conducting. In other words, the conducting state has been transferred from tube T-2 to T-I, and this condition will persist indefinitely, in the absence of another negative pulse. When now a second negative pulse is applied to the two grids, the triggering action is again produced in the opposite direction, transferring the conducting state back to tube T-2. Obviously, when a continuous train of spaced negative pulses is applied to the two grids, Ithe two tubes will be periodically and alternately conducting and non-conducting, the condition of the system periodically repeating itself for each two pulses. Thus, if the input pulse frequency is j, pulses having the frequency of f/2 will be produced in the branch circuit of each tube. These pulses of half of the input frequency may be transferred to the second stage by means of lead wire I3 connected to the grids of tubes T-3 and T--4 through input condensers C|r3 and C-|`!, causing similar reversals of conduction and non-conduction of these tubes at half the rate, producing pulses of the frequency f/2 in the branch circuits of each tube. Finally, these pulses of one-fourth of the original input frequency may be transferred to the third stage by means of lead wire I4 connected to the grids of tubes T-5 and T-6 through condensers C-23 and C-ZT, again causing similar reversals of conduction and non-conduction at half the rate of that of such reversals in the second stage, producing pulses of the frequency of f/B in the branch circuit of the third stage. Of course, if desired, negative pulses may be transferred to a fourth stage (not shown) through lead l5 and from this fourth stage to a fifth stage, and so forth, to cause further frequency division by the factor of 2 by each subsequent stage.

From the foregoing considerations, it is clear that when negative pulses of appropriate Value, generated by master pulse generator I6, and having the frequency f are introduced into the first stage through input lead 20, pulses of the frequency of f/Z, f/i4 and f/8 will be respectively produced in the first, second and third stages of the cascaded system. In other words, the cascaded stages will operate as an aperiodic frequency divider system, producing a group of octavely related pulse frequencies in the several stages. These octavely related pulses may be selectively or collectively withdrawn for introduction into a common output circuit including an amplifier lil-l and loud speaker L-l.

Considering now cathode drop resistances R-, R-S, R-IS, R-IB, R-28, R-29 connected in series with the cathodes of tubes T-I to T-B, respectively, their presence in the cathode circuits will not in any way disturb the balance of the individual stages, nor will it appreciably affect the described operation of the individual stages or of the entire cascaded system in view of the relatively low value of these resistances in comparison to the total resistance in the plate circuit of each tube. Their presence in the cathode circuits will merely raise the average cathode potentials slightly above ground potential and will provide points of fluctuating potential from which output pulses of the desired frequencies may be conveniently withdrawn into a common output circuit.

Thus, upon actuation of switching key S-I, the cathode of tube T-2 is connected to output bus bar I9 through small coupling condenser C-S and decoupling resistance R-IIL An output pulse having the frequency f/2 will be introduced into amplifier K-|, and the amplified pulses will be made audible in translating means or speaker L-l. Actuation of switching key S-2 will connect the cathode of tube T-d to the output bus bar I9 through condenser C-IS and resistance R-ZU, while actuation of switching key S-3 will connect the cathode of tube T-G to the output bus bar i9 through condenser C-29 and resistance R-30, thereby introducing pulses of the frequency f/4 and f/8, respectively, into the amplifier. Of course, the switching keys S-l, S-Z and S-3 may be selectively or collectively actuated, simultaneously or in any desired sequence, so that sounds corresponding to any desired combinations of the aforesaid frequencies may be produced in the speaker at the same time.

The output condensers 0 9, C-IS, and C-29 are merely provided for the purpose of isolating the direct current component of the output pulses from the amplifier. Their Value may be from 0.00001 to 0.005 microfarad and is by no means critical. The provision of decoupling resistances R-I0, R-20 and R-S has the object of decoupling the common output circuit from the individual stages and thereby to prevent undesirable reflection of pulse energy from one stage into one or more of the others, in case more than one of the switching keys S-l, S--2, S-3 is actuated at the same time. The value of the decoupling resistances is not critical, in general they should be appreciably higher in value than the cathode resistances, and their value may be in the order of 10,000 to 100,000 ohms. The value of the coupling capacitors and of the decoupling resistances, of course, has considerable effect on the amplitude of the pulses withdrawn and to some extent also on the waveform of the said pulses. By coordinating appropriate but in general different values of these elements to the several stages, it is possible to balance the output energy and waveform throughout the entire range of the instrument and also to compensate for the uneven frequency response of the ainplifier and speaker, as this is set forth more fully, for example, in my U. S. Patent No. 2,252,189, to which hereby reference is made.

The master pulse generator may be of any desired type, the only important consideration being that it should have a reasonably constant frequency, or its frequency be adjustable in steps to a predetermined number of different frequencies, in themselves constant. It also should be capable of generating negative pulses in the order of about l0 to 40 volts. In general sharp pulses are to be preferred and may be obtained from a great variety of different devices, such as from relaxation oscillators of both the gaseous or vacuum tube type, blocking oscillators, square-Wave generators, and the like. It is also possible to employ master oscillators producing substantially sinusoidal oscillations and then to convert these oscillations into sharp pulses of lthe desired character by means of pulse-sharpening circuits involving tubes in appropriate circuits or only a suitable network formed of condenscrs and resistances. A simple pulse sharpening circuit comprising condenser C-o and resistance R-o is shown in Fig. l, although, of course, in most cases more complex circuits will be employed. In view of the fact that the art of pulse generation, including the various oscillator and pulse sharpening circuits is well known to those skilled in the art and does not constitute any 9 (meuf-theobjectsv of theinvention, no .detailed description of the 1various possible circuit arrangements is believed Ito be necessary.

It .will be noted that the electrical musical instrument embodying the principles of the present inventionprovides numerous important advantages which could notbe obtained, or even approached,` heretofore. Thus, it is to be observedat the outset, that the cascaded system of frequency-halving stages, each. of which comprises a. ,pair of space discharge devices connected in a trigger circuit having two stable states of equilibrium, `constitutes a frequency dividing network which iscompletely aperiodic in character andoperationfat least over the entire audiofrequency range. The individual stages, as well as the entire system,.are incapable f producing oscillationsindependently from an input signal or pulse. .In the .absence of any input signal or pulse, each of the severalstages will assume one of its stable states of equilibrium. In this condition no output signalcan be produced, whether intentionally or unintentionally, and the output circuit and the speaker vassociated therewith remaincompletely inoperative even in case one, or more, of the` switching keys S-I, S-2 or S-3 wouldbe operated. This is of greatimportance in the construction of practical electrical .musical instruments since it assures complete freedom from background noise and from the production of non-harmonic.v notes which are-so difcult to .avoid .inconvention-al electrical musical .instruments employing cascadecl. oscillator stages, .each of which iscapable of the production of independent oscillations.

Under any .and all operating conditions the pulses produced in the. several stages .are octavely related to .each other and tothe input pulse. If ,the vinputpulsefrequency is varied, whether in steps or continuously, the outputpulses drawn from the several stages will likewise vary with it, always retaining, however, the said octave relationship without any adjustment of the circuit constants, which was necessary in prior, nottruly aperiodic, frequency-dividing systems. In other words, .an electrical musical instrument based on the principles of the present invention can never getout .of tune and Will voperate in the correct pitch at all times, even though the circuit constants, .the .characteristics of the tubes, or the operating voltages be changed to a very substantial degree. Thus, experiments have indicated that the instrument will perform completely satisfactorily and in an entirely stable and dependable 'fashion with possible variations of the plate .orbiasing voltages ashigh as plus or minus "20%. Of course, nothing even remotely approaching this extreme stability could be .obtained in prior electrical musical instruments employing cascaded systems of the not truly aperiodic type.

The output pulses drawn from any one of the stages are of substantially equal voltage as they 'are largely determined lby the cut-off characteristics of thetubes and not by the frequency, at least Within the practical or audio-frequency range. The lwaveform vof the saidpulses is 'characterizedvby extremely sharp rise ofthe wave front and a corresponding `rapid decline at the end of eacnpulse. Experience rhas demonstrated that this waveform is very advantageous in electrical musical instruments due to thepresence of a substantially unbroken series ofi harmonics therein. An infinite variety of waveforms of lower-.harmonic content may be derived 'from the original outputpulses by means of simple filter circuits and the modified waveforms, when converted into musical sounds, are capable of simulating the tone colors of practically all known musical instruments and organ stops, as this is clisclosed, for example in my copending application, Serial No. 463,291, led October 24, 1942, now Patent No. 2,403,664, dated July 9, 1946.

It will be noted that in the circuit illustrated in Fig. 1, the highest output frequency, which may be withdrawn, is the one obtained by the actuation of switching key S-l and has a frequency f/Z, corresponding to one-half of the frequency f of the master pulse generator I6. In other words, the frequency range of the instrument starts one octave lower than that of the master generator and covers a number of triggered frequency-halving stages. Of course, it would be easilypossible to directly utilize the output of the master generator, by means of an additional switching key coordinated thereto, and thereby to add one more octave to the range, corresponding to the frequency f. In view of the fact, however, that in general the waveform of the master generator pulses may be quite different from that of the output pulses, it has been found to be desirable to follow the practice indicated in the drawing whereby output pulses are drawn only from the frequency-halving stages. In order to cover the full musical range ofthe instrument, in that case, the frequency of the master pulse generator has to be twice the frequency o'f the corresponding note of the highest octave of the instrument. This, however, does not involve any practical dificulties, since the triggered frequency-halving circuits described in the foregoing are capable of dependable operation well over any frequency Which may be required in a musical instrument and, as a matter of fact, will perform quite satisfactorily up to the lower radio frequencies.

In general, in a practical musical instrument, the switching keys S-l, S-Z, and S-3, etc., are arranged as, or are. coordinated to individual keys of a playing manual, preferably similar to that of a conventional key board instrument, such as a piano, or an organ.

The principles of the invention may be applied to the construction of electrical musical instruments of greatly different type which may be broadly divided into two distinct classes; to wit: melody instruments and chord instruments. Melody instruments are capable of producing only one musical note at a time, while chord instruments are free from this limitation and are capable of producing any desired combination of musical notes simultaneously. Melody instruments may comprise a single series of cascaded frequency-halving stages and a single master pulse generator, which'is'tunablein steps t0' any tempered note of a single octave. Chord instruments require in general a large number of series of cascaded stages, for example one for each tempered note of a single octave, and a master pulse generator of constant frequency for each of said series as this will be set forth more fully hereinafter.

Fig. 2 is the. circuit arrangementof an electrical musical instrument of themelody typeand embodying the principles of the present invention. For the sake ofsimpiicity an instrument having a range of' 3 octaves has been illustrated and described, 7 notes Abeing provided for each octave in accordance with the seven steps of the diatonic scale. Of `course,in a practical melody instruil filent of this type generally a wider musical range would be provided, such as 5 or 6 octaves, and the tempered scale including twelve notes or steps in each octave would be used, as those skilled in the art will readily understand.

The instrument essentially comprises three stages of frequency-halving trigger circuits of the type shown in Fig. 1 and represented by blocks O I, 2 and 0 3, respectively. Input pulses of a frequency f may be introduced into rst trigger circuit 0 I, which is coupled to the second trigger circuit 0 2 through lead 42, this in turn being coupled to the third trigger circuit 0 3 through lead 43. If desired, additional trigger circuits (not shown) may be connected to 0 3 through coupling lead 44. Pulses of a frequency f/2 may be drawn from circuit O l through output lead 45, pulses of a frequency of f/4 may be drawn from circuit 0 2 through output lead 46, and, finally, pulses of a frequency /8 may be drawn from circuit 0 3 through output lead 41, as this has been set forth more fully in the description of the circuit of Fig. 1 of which this portion of Fig. 2 is a diagrammatic representation.

` It will be noted that to each note of the range of the instrument there are coordinated tWo superposed switches or switching keys, arranged for joint operation by a common keyy or the like. The upper row of these switches, S-Il to S-31, are the octave-determining switches, which are divided into three groups S-Il to S-ll; 2! to S-Zl; and S-SI to S-Sl. The switching arms of the first group of switches S Il to S |l are all connected to output lead 4l of trigger circuit 0 3, the switching arms of the second group of switches S 2| to S 2`I are all connected to output lead 46 of trigger circuit 0 2, and the switching arms of the third group of switches S-SI to 8 3'1 are all connected to output lead 45 of trigger circuit 0 1. The working contacts of all of the switches S |l to S 3 are connected to a common output bus bar 48, which introduces the output pulses into amplifier K 2, the amplified pulses being converted into musical sound by means of a loudspeaker L 2.

Directly underneath the row of octave-deter mining switches S l i to S 3'rl, there is provided a corresponding row of note-determining switches 8 4! to S 5'l. A mechanical connection indicated by dotted lines is provided between pairs of superposed switches so that they may be jointly actuated by an operator, such pairs being S-i I and S 4l; S i2 and 8 42; S |3 and S 43; and so forth to S 3l and 8 5?. rlhe said pairs of switches or switching keys may in themselves constitute the playing manual, or may be coordinated to keys of a playing manual, as those skilled in the art will readily understand.

The note-determining switches are likewise divided into three groups, S 4l to S 41; S 5l to S 51; and S 6l to S 6'l. The switching arms of all of the switches S 4I to S 61 are connected to a common bus bar 49. The working contacts of switches S 4l; S 5l and S--Sl are connected together by means of a bus bar 50, those of switches S 42; S-52 and S 62 are connected together by means of a bus bar 5|; and so forth to the working contacts of switches S 41, S 5'l and S 61, which are connected together by means of bus bar 56. In other words, working contacts of the switches corresponding to the same notes of the octave ln the several octave groups are connected together by means of bus bars 50 to 56, respectively.

A resistance R/ 4I is connected between bus bars 50 and 5I, a similar resistance R 42 is connected between bus bars 5| and 52, and so forth, one such resistance being connected between adjoining pairs of bus bars up to resistance R 46, which is connected between bus bars 55 and 56.

Reference character P generally denotes a master pulse generator comprising a glow-dis charge tube N, a condenser C 4I and a source of direct current M, all connected serially and in the same circuit. The junction point of condenser C 4I and source M is grounded and is connected to bus bar 56 through a resistance R 41, The other terminal of condenser C 4l is connected to bus bar 49 and also to lead wire 4l, which is the input lead of the cascaded frequency-dividing system 0 l, 0 2, and 0 3.

To understand the operation of the entire lnstrument, it is to be appreciated at the outset that the system N, M, C 4l constitutes a relaxa-f tion oscillator of the glow-discharge tube type capable of producing sharp pulses of predeter. mined frequency when a resistance of appropriate value is connected across condenser C 4I. For further details of the construction, circuit constants and operation of relaxation oscillators of this type reference may be had to my U. S. Patent No. 1,993,890. For the purposes of the present description, it will be suicient to state that the value of resistances R 4| to R 41, the capacity of condenser C 4l and the voltage of direct current source M are so determined that by connecting an appropriate number of the said resistances across condenser C 4l, the output frequency of generator N may be adjusted to any one of the steps of an octave of the musical scale, one octave above the highest octave of the range of the instrument. 0f course, it is also possible to employ any other suitable type of oscillation or pulse generator, capable of being tuned in steps to the several steps of an octave of the musical scale.

Assuming now, for example, that switches S-H and S 4l are jointly and substantially simultaneously closed by means of a suitable operating mechanism, such as by depression of the corresponding key of the playing manual, S 4l will connect all of the resistances lib-4Iv to R-41 across condenser C 4I, through bus bars 49 and 56. This will practically instantaneously cause the generation of pulses by the pulse generator P, having a frequency one octave above the highest C note of the range of the instrument. These pulses will be introduced into the frequency dividing system O l, 0 2 and 0 3. The output derived from frequency-halving stage 0 3 will have a frequency equal to one-eighth of the input frequency, corresponding to note C I. This output will be introduced into amplifier K 2 through closed switch S-Il and bus bar 48 and will produce a musical sound corresponding to the note C I in speaker L-2.

Actuation of the pair of switches S 2| and S 5| will cause the production of the note C II in the speaker. This will be readily appreciated if it is considered that although closing of switch S-5l will tune the master pulse generator P to the same frequency as S 4l, the output will now be withdrawn from stage 0 2 through closed switch S 2l. Therefore, the output signal will be merely one-fourth of the input frequency, corresponding to note C II, which is one octave higher than note C I. Likewise. actuation of gaseosa' switches S 3I and S 6I will cause the production of the note C III, because generator P will be tuned to an octave above C III by means of switch C Gl, whereas output will be drawn from stage O I through closed switch S 3l, after a single frequency-halving operation,

When any other pair of switches is actuated, the lower or note-determining switch will always tune the pulse generator to the corresponding note of its one octave range, while t-he simultaneously closed upper or octave-determining switch will always withdraw signal which has been subjected to the proper number of frequency-halving operations. Thus, for example, when the pair of switches S-24, S 54 is closed, the latter will connect resistances R-44 to R 41 across condenser C 4I through bus bars 49, 53 and 56, thereby tuning generator P to a note F, one octave above the highest F of the instrument. Switch 24, on the other hand, will draw output pulses from stage 2, one-fourth in frequency o1 that of the input pulse, resulting in the production of note F II in the speaker. From the foregoing considerations it is clear that the actuation of any pair of switches will produce the desired note in the speaker throughout the entire range of the instrument.

The circuit just described is primarily in tended for the purposes of a melody instrument producing only one musical note at a time. Therefore, in general, only one pair of the switches will be actuated or closed at any time. It is to be observed, however, that even the accidental or intentional actuation of several pairs of switches simultaneously will not produce any unharmonic or musically undesirable notes.` The simultaneous actuation of the two note-determining switches will merely tune the pulse generator to the higher note of the two within the octave range. The simultaneous actuation of the two corresponding octave-determining switches will draw output from one of the Oy stages when the two pairs of switches are within the same octave, and will draw output from two of the said stages when the said pairs are within different octaves. ln the first case the output will be a single note, corresponding in note and octave relation to the higher one of the two pairs oi switches, while in the second case two octavely related notes will be simultaneously produced the note frequency of which will be determined by the higher one of the actuated pairs of switches while their octave position is respectively determined by each of the said pairs of switches.

A musically desirable result of this peculiarity of the instrument is that two or even three octavely related notes may be produced simultaneously by actuation of the corresponding pairs of switches.

Fig. 3 is the circuit diagram of a modified electrical musical instrument of the melody type embodying the principles of the present invention. It will be noted that the switching arrangement shown in this ligure is practically identical with that ci Fig. 2, and that the difference resides in the coordination of the switching elements and of the pulse generator to the frequency dividing system.

The instrument essentially comprises an upper set of octave-determining switches S Il to S-Sl, divided into three octave groups, and a lower set of note-determining switches S 4l to 5 6?, likewisedivided into three octave groups.

Corresponding pairs of switches in the rtwo sets are mechanically connected for joint operation by keys of a suitable playing manual, as indicated by dotted lines in the drawing. The lower setof switches S 4l to 5 6? is electrically associated with resistances lit-4| to R 4'l and with pulse generator P. In view of the fact that this portion of the circuit is substantially identical with the corresponding portion of Fig. 2, and since similar reference characters have been used to denote corresponding elements, no repetition of the description of its structure and operation will be necessary.

Considering now the output circuit of the instrument, it comprises a series of cascaded aperiodie irequency-halving stages 0 4, 0 5, and 0 6, which are similar to the ones described in connection with Figs. l and 2. The rst one of these stages, 0 4, is coupled to the second stage, 0 5, through a lead 58, and this second stage is coupled through a similar lead 5l to the third stage, 0 6. The output of stage 0 6 is directly introduced into an amplifier K 3, the amplified pulses being converted into musical sound by means of a speaker L 3. If desired, additional frequency-halving stages may be connected ahead of stage 0 4 by means of a lead wire 59. Unidirectionally conducting elements Q l and Q 2, may be connected in leads 5l and 53, respectively, for reasons which will appear presently. These elements are preferably of the well known dry rectifier type although any other suitable type of rectiiier, for example a diode, may be used with equal or similar results.

The switching arms of octave-determining switches or switching key S-ll to S l'l are all connected to a common bus bar 4l, which is in communication with the input lead 59 of the iirst frequency-halving stage 0 4 through lead 62. The switching arms of the second group of octave-determining switches S 2l to S-Zl are all connected to a common bus bar 46, which is in communication with input lead 58 of the second frequency-halving stage 0 5 through lead 6I. Finally, the switching arms of the third group of octave-determining switches S 3l to S-Sl are all connected to a common bus bar 45, which through lead 60 is in communication with input lead 5l oi the third frequency-halving stage 0 6.

The working contacts of all octave-determining switches S-I l to S-Sl are connected to the same bus bar 48 which is in communication with pulse generator P through lead 4I and has an alternating potential impressed thereon whenever pulses are produced by the generator.

Considering now the operation of the instrument, it will be immediately noted that whenever a pair of coordinated switches is closed, the lower one of the two will connect a predetermined number of the resistances R, 4l to R 41 across condenser C 4l of pulse generator P and thereby tune the said generator to one of the notes within the one-octave range of the generator, as this has been described more fully in connection with Fig. 2. Thus, bus bar 48, connected to the working contacts of all of the octave-determining switches, will be energized by pulses of corresponding frequency.

At the saine time, however, when one of the note-determining switches is closed, the corresponding octave-determining switch of the pair will be likewise closed, due to the mechanical connection of the said switches. The circum-v stance whether this octave-determining switch is in the first, second, or third octave group will determine the point where the pulses will be introduced into the series of cascaded frequencyhalving stages. If pulses of the'frequency are introduced into the series through lead 59, the input frequency will be halved in frequency three times, producing a note of a frequency of f/B in the speaker L-3. Pulses of the same frequency introduced into the series at lead 58 or '51 will be halved in frequency twice, or once, respectively, producing a note of a frequency f/4 or f/Z in the speaker.

Thus, for example, when the pair of switches S-I6, S46 is closed, the lower one, S-46, will connect resistances R-/ii and R-l'l across condenser C-lll and will tune pulse generator P to the note A within its octave range. The simultaneously closed upper switch S-IB will introduce these pulses into input lead 59 so that its frequency halved three times in succession will produce the lowest A note, A-L of the range of the instrument in the speaker. Closing the pair of switches S-ST and S-El will tune the pulse generator to its note B, and cause halving 0f the pulse frequency only once, thereby producing the note B-III, the highest B of the range of the instrument. It will be noted that by operating the corresponding pair of switches, any note within the range of the instrument may be produced in the speaker.

Preferably, the octave within which the pulse generator may be tuned in steps is so determined that it is one octave above the range of the instrument. The range of the instrument may be extended downwards by any desired number of octaves by connecting additional frequency-halving stages ahead of stage 0 4 and a group of switches for each additional stage.

The object of the provision of rectiers Q-I and Q--2 between adjoining cascaded frequencyhalving stages is to prevent the pulses intended for introduction into the stage ahead entering the preceding stage. They permit the transfer of pulses in the proper direction from one stage to the next one but prevent the now of pulses in the opposite direction. However, the provision of these rectiflers is not absolutely necessary and in some cases the desired operation may be obtained merely by properly adjusting the circuit constants, biasing voltages, etc., of the cascaded stages.

Fig. 4 illustrates the circuit diagram of a polyphonic electrical musical instrument or electrical organ embodying the principles of the present invention.

Generally speaking, a polyphonic instrument, that is an instrument capable of producing any desired plurality of musical notes at the same time in the form of musical chords, may be built by providing a number oi series of cascaded frequency-halving stages, and a master pulse generator of constant frequency for each of said series. Thus, in the simplest case, twelve master pulse generators may be provided, each being tuned to a different note of the tempered scale, one octave above the highest octave of the instrument, such as C. Ct, D, Dt, E, F, Fil, G, Gt, A, At and B. A series of cascaded frequency-halving stages of the type shown in Fig. 1 is provided for each of the twelve master pulse generators, each series producing all of the octavely related notes of the frequency of the master pulse generator. A switching key may be coordinated to each of the said octavely related notes and may be utilized to withdraw output pulses for introduction into a common output circuit comprising an amplifier and a loudspeaker. The switching keys may be arranged in the form of a conventional organ playing manual which may be operated in the usual manner to play any desired musical composition.

This fundamental form of electrical organ embodying the invention requires 12 series of cascaded frequency-halving stages. It has been discovered that by using modified and improved circuits, the number of requency-halving series may be reduced with attendant considerable saving in cost and space. An improved circuit of this type is shown in Fig. 4 and is based on the peculiarity of practically all known musical compositions that a note and the next note of the tempered scale half a tone removed therefrom will be rarely, if ever, required at the same time. Thus, for example, C and Ct; D and Dil; E and F, Ft and G; Gt and A and finally All and B will not be ordinarily required simultaneously. This simple consideration permits a reduction in the number of frequency-dividing series from 12 to 6, cutting the cost of construction practically in half.

For the sake of simplicity, the circuit of Fig. 4 has been shown as having a range of only three octaves and only 6 notes of the tempered scale have been shown in each octave, to wit: C, Ct, D, Dt, E and F. Of course, in a practical instrument or organ the range will be considerably greater, usually 5 to 7 or 8 octaves, and obviously 12 tempered notes are provided in each octave corresponding to the chromatic scale of equal temperament now universally used in Western music.

Referring now to Fig. 4, there are shown therein three series of cascaded frequency-halving stages, the rst of said series comprising stages O-'l, O-8 and O-9, the second comprising stages O-i0, O-ll and O-l2, and the third comprising stages O-l3, O-l4 and O-I 5. Lead 1| is the input lead of stage O-1, which is coupled to stage O-8 through lead 12, stage O-8 is coupled to stage O-9 through lead 13; lead 14 being the output lead of stage 0 9. Likewise, leads 'I5 and 19 are the input leads of stages O-I ll and O-l3, respectively, which are coupled to stages O-II and O-IA through leads 16 and 80, respectively. Stages O--| l and O-l4 are coupled to stages O-I2 and O-l5 through leads 11 and 8l, respectively, leads 'I8 and 82 being the output leads of stages O-I2 and O-I5, respectively.

The switching arrangement of the instrument comprises an upper row of octave-determining switches S-ll to S-9S, divided into three octave groups S-'il to S-16, S-Sl to S86 and S-9I to S-SS, and a lower row of note-determining switches S-Illl to S-I26, likewise divided into three octave groups S-llll to Sl06, S-l Il to S-IIB and S-I2l to S-|26. It will be noted that each octave-determining switch is mechanically connected to the corresponding and directly underlying note-determining switch, as this is indicated in the drawing by dotted lines, so that the corresponding switches may be jointly operated in pairs by keys of a playing manual.

The switching arms of the octave-determining switches are connected in pairs, each pair being connected to a corresponding coupling lead between adjoining frequency-halving stages through a decoupling resistance R-5'l, so that upon closure of the switches, output pulses of desired frequency may be withdrawn from the sev- 'i7 eral stages. The connections of the said pairs of switches will appear from the following table:

S-1l and S-12 are connected to output lead 14 S-13 and S-14 are connected to output lead 18 S-15 and S-TS are connected to output lead 82 S-SI' and S-82 are connected to coupling lead 13 S-83 and S-il are connected to coupling lead 11 S-85 and S--Bi are connected to coupling lead 8| S-SI and 92 are connected to coupling lead 12 S-93 and S-S are connected to coupling lead 16 S-QE and S-Q are connected to coupling lead 80 The working contacts of all of the octave-determining switches S-! to S-S are connected to a common output bus bar 8S whereby the collected output pulses of various different frequencies may be jointly introduced into amplifier K-4. The amplied pulses are rendered audible by a loudspeaker L-ll.

The note-determining switches are likewise interrelated with each other by means of suitably arranged leads or bus bars. Thus, the switching arms of all of the note-determining switches S-llll to S-IZB are connected together by means of a grounded bus bar 84. The working contacts of the note-determining switches corresponding to the same note of the tempered scale in the several octave groups are likewise connected together by means of bus bars, as this will appear from the following table:

S-Il, S-|||, S-l2l vare connected by bus bar 85 S-I02, S|l2, S-l22 are connected by bus bar 8B S-I03, S-IIS, S-l23 are connected by bus bar 81 S-|04, S-IM, S-I24 are connected by bus bar 88 S-I05, S-II5, S-l25 are connected by bus bar 89 S-IDB, S-IIS, S-I2S are connected by bus bar-90 A resistance lit-54 is connected between bus bars 85 and 8B, a resistance R-55 is connected between bus bars 81 and 88, and a resistance R-56 is connected between bus bars 8S and 90.

The input pulses for the three series of frequency-dividing stages are produced by three glow-discharge tube relaxation oscillators P-l, P-Z and P-3, respectively comprising glow-discharge tubes N|, N-2 and N-3, and series condensers C-5|, C-52, and C-53, all of which are connected across a common source of direct current M-I, the positive terminal of which is connected to bus bar 84 and is grounded. A resistance R-5l has one of its ends connected to the junction point of tube N-l and condenser C-l, While its other end is connected to bus bar 86. Similar resistances R-52 and 12H53 have one of their ends connected to the junction points of tubes N-2 and N 3 and condensers C-52 and C-53, respectively, while their other ends are respectively connected to bus bars 88 and S8.

Resistances R-SI and R-54 are so determined with respect to condenser C-5l and to the other circuit constants of pulse generator P-i that when switch S-i2l is closed and both resistances are connected across the said condenser, pulses of a frequency one octave above the highest C of the instrument will be produced. Of course, the same occurs when switch S-ll or S-l I I is closed, since the said switches are in parallel with S-IZL On the other hand, the value of R-S'I is so determined that when one of 18 the switches S-I22, S-IIZ or S-IUZ is closed and only R-5i is connected across condenser C-5l, pulses of a frequency one octave above the highest Ct of the instrument will be produced.

lt may be also noted here that when both S-lZl and S-i22 are closed at the same time, only R-Si will be connected across condenser C-5i, while R-S will be short circuited, so that the pulse generator will be adjusted to the same frequency as when S-l22, the higher one ofthe two switches, is-alone closed. In other words, of two simultaneously actuated switches associated with the same generator the higher one of the two is controlling so that at no time are any nonharmcnic notes produced. The same is true, vof course, with respect to resistances R-52 and R-55 or R--53 and Rf-56 which may be individually or jointly connected across condensers C-iZ and C*53, respectively, by the corresponding switches.

From the foregoing description, theoperation of the polyphonic instrument illustrated in Fig. 4 will be readily understood. Whenever any one of the pairs of mechanically connected switches is closed, the lower one of the two, the note-determining switch, will adjust one of the pulse generators to the proper note frequency and the pulses of such frequency will be introduced into one of the frequency-dividing series. The upper, or octave-determining switch, at the same time will withdraw pulses at such point of the series that a musical sound in the proper octave relation to the input pulses will be produced in speaker L-4, as a result of such withdrawnpulses being introduced into amplifier K-4 through bus bar 83.

Thus, if the pair of switches S-1l and S-Il is closed, switch S-ll will connect resistances R-5l and R-S across condenser C-5I and will adjust pulse generator P-l to note C, one octave above the highest C of the instrument. At the same time, switch S-1I will connect frequencyhalving stage O-9 to amplifier K-4 through output lead 14, one of the decoupling resistances R-Sl, and bus bar 83. The input pulse derived from generator Pei will be halved in frequency three times, producing note C-III in the speaker, three octaves below the input frequency. When one of the pairs S8| and S-l Il or S-Sl and S-l2l is closed S-III or S-I2l will tune P-l to the same note frequency as before but output will be withdrawn from stages O-8 or 0 1, respectively, producing note C-II or C-III, respectively, which are one and two octaves higher than C-l. It is also possible, of course, to produce C-I, C-II and C-III simultaneously, by closing the corresponding pairs of switches simultaneously in which case output pulses will be withdrawn from different points of the frequency-dividing series. In that case, the decoupling resistances R-51, which may be in the order of 5000 to 50,000 ohms, prevent direct transfer or reflection of pulse energy from one stage to the other which otherwise might interfere with the proper operation of the frequencydividing series.

From the foregoing considerations and from the circuit illustrated in Fig. 4 it is clear that when any pair of switches is closed successively or simultaneously, the lower ones of the switches will always adjust the corresponding pulse generators to the proper input frequencies while the upper ones will always withdraw pulses at such point of the frequency-dividing series that the desired notes will be produced in speaker L--L n this manner, by actuating the switches in the proper sequence, any desired musical composition may be played. The only limitation is that when pairs of switches corresponding to the notes C and Ct, D and Dt, E and F, Ft and G, Gt and A or At and B are simultaneously closed, only Ct, Dt, F, G, A and B, respectively, will sound. This limitation, however, will be hardly if ever noticeable in executing conventional musical compositions and is well compensated for by the substantial reduction in the cost of the instrument. rlhis limitation, oi course, may be avoided by providing twelve master pulse generators, one for each note of the tempered scale, and by assigning a separate frequency-dividing series to each note.

While the pulse generators shown in Fig. 4 are of the glow-discharge tube oscillator type, any other suitable pulse generator or oscillator may be used, such as those employing vacuum tubes, provided that they are capable of producing sharp negative pulses of suiiicient voltage.

In the circuit illustrated in Fig. 1, the output pulses are withdrawn at the cathodes of tubes T-2, T-d and T-6. This arrangement has the advantage of providing an extremely loose coupling between the several stages and the common output circuit. Of course, it is also possible to withdraw output pulses from any other suitable point of the several stages, such as, for example, from the plates, from a suitable point on the set of resistors R-4, R-5, R-I and R-l and of the corresponding sets oi resistors in the other stages, or from the coupling leads I3, I4 and I5. In each case it is desirable to interpose a suitable network, such as an output condenser and a decoupling resistance, between the points of withdrawal of the pulse energy and the common output circuit.

In Fig. 2 wherein O-I, O-2 and 0 3 are representing the frequency-halving stages, output leads 45, 46 and 4l stand for such suitable output connections in the several stages. In Fig. 3, coupling leads 59, 58 and 51 are connections between adjoining stages which correspond to coupling leads 20, I3 and I4, respectively, in Fig. l.

Likewise, in Fig. 4 leads 1I, 'I2 and 13; 15, 'I6 and T1, "I9, 8D and 8I respectively, correspond to leads 2U, I3, and I4 in Fig. 1.

Switching keys S-I, S-2 and S-3 in Fig. 1 are preferably constructed and arranged as keys of a conventional playing manual, similar to that of an organ. In the instruments shown in Figs. 2, 3 and 4, where pairs of circuits are simultaneously operated for each note, the desired simultaneous actuation of a pair of switches is preferably obtained by coordinating two pairs of electrical contacts to each key of the playing manual, as this is customary in electrically controlled pipe organs.

In the frequency-halving trigger circuits illustrated in Fig. l, a pair of high vacuum triodes is used in each of the stages. Of course, it is also possible to employ various other forms of trigger circuits with equal or similar results such as the modified Eccles-Jordan circuit employing a pair of high vacuum pentodes for each stage, or the Wynn-Williams pulse counting circuit employing a pair ci gas triodes for each stage.

Although the present invention has been disclosed in connection with a few preferred embodiments thereof, variations and modifications may be resorted to by those skilled in the art without departing from the principles of the invention. I consider all of these variations and modifications to be within the true spirit and scope of the present invention as disclosed in the foregoing description and defined by the appended claims.

What is claimed is:

l. An electrical musical instrument comprising in combination a series of cascaded frequencyhalving stages having aperiodic characteristics over the audio frequency range, each of said stages including a pair of space discharge tubes connected into a trigger circuit having two stable states of equilibrium, a master pulse generator operatively associated with the first stage of said series tunable to frequencies corresponding to tempered notes within one octave of the range of the instrument, a set of primary switching means for selectively adjusting the frequency of said generator thereby causing the generation of pulses in the several stages the frequency of which is octavely related to the frequency to which said master pulse generator is adjusted, an output circuit, a set of secondary switching means interposed between said output circuit and said stages for selectively introducing pulses of desired frequency from said stages into said output circuit, a playing manual having keys each capable of concurrently actuating a primary and a corresponding secondary switching means whereby the said primary switching means will determine the note and the said secondary switching means will determine the octave of the pulses introduced into the output circuit, and translating means responsive to the pulses in said output circuit for converting said pulses into musical sound.

2. An electrical musical instrument comprising in combination a series of cascaded frequencyhalving stages having aperiodic characteristics over the audio-frequency range, a pulse generator, switching means for selectively introducing the output of said generator into any one of the said stages thereby producing pulses of octavely related frequencies in the following stages, and translating means for converting pulses produced in the last one of the said stages into musical sound.

3. An electrical musical instrument comprising in combination a series of cascaded frequencyhalving stages having aperiodic characteristics over the audio frequency range, each of said stages including a pair of space discharge tubes connected into a trigger circuit having two stable states of equilibrium, a, pulse generator having a frequency adjustable within the range of one octave, switching means for selectively introducing the output of said generator into any one of the said stages thereby producing pulses octavely related to the input frequency in the following stages, unidirectional coupling means interposed between adjoining stages to prevent the introduction of input pulses into stages preceding the input point, and translating means associated with the last stage to convert the pulses produced therein into musical Sound.

I1i. An electrical musical instrument comprising in combination a series of cascaded aperiodic frequency-halving stages, each including at least one space discharge tube connected in a trigger circuit having two stable states of equilibrium, a pulse generator, a set of tuning elements for said generator adapted to adjust the frequency thereof in steps to frequencies corresponding to successive notes of the tempered scale within the range of a single octave, a multi-octave keyboard, a jointly operable primary and a secondary switch for each key of the said keyboard, said primary switch being operable to selectively connect a assenso corresponding tuning element of said set to said generator 'thereby to adjust the frequency of said generator in accordance with the position of the key within its octave and said secondary switch being operable to selectively introduce the output of said generator into one of the said stages in accordance with the position of the said octave with respect to the several octaves of the range of the instrument, and translating means connected to the last one of the said stages for converting the pulses therein into musical sound, the frequency of said sound being adjustable in steps to any tempered note within the range of the instrument.

5. An electrical musical instrument comprising in combination a series of cascaded frequencyhal-ving stages of the triggered type having aperiodic characteristics throughout the audio frequency range, a generator operable to deliver pulses to the first one of said stages at a frequency adjustable in chromatic steps within a single-octave range, a set of note-determining switches grouped in accordance with notes of the octave, a system of tuning elements under control of the said switches for selective connection to said generator to adjust its frequency to the corresponding note of the octave, a set of octavedetermining switches grouped in accordance with octavos, said sets having corresponding pairs of switches therein arranged for joint operation, a, common output circuit, connections between the groups of octave-determining switches and the respective frequency-halving stages to withdraw pulse energy of appropriately reduced frequency therefrom, and connections between all of the octave-determining switches and the output circuit to render pulse energy withdrawn from any one of the said stages effective in said circuit.

6. An electrical musical instrument comprising in combination a series of cascaded pulse-counting frequency-halving trigger stages, each of said stages being responsive to a train of input pulses of any audio frequency by the transfer of pulses at half of such frequency to the next stage, means for selectively introducing input pulses into one of said stages, means for withdrawing output pulses at reduced octavely-related frequencies from at least one of the following stages at a time, an output circuit, switching means for making the withdrawn pulses selectively effective in said circuit, and decoupling means interposed between the points of pulse withdrawal and the said switching means to substantially prevent the reflection of pulse energy from the said output circuit into the said stages.

7. An electrical musical instrument comprising in combination a group of six series of cascaded aperiodic pulse-counting stages, each of said stages being responsive to a train of input pulses by the transfer of pulses at half the input frequency to the next stage, a master pulse generator for each of said series and adapted to supply input pulses thereto, jointly operable primary and secondary switches for each chromatic note of the multi-octave range of the instrument, tuning means under the control of said primary switches to selectively tune said generators to one of two notes a half-tone apart in accordance with the notes of the operated switches so that the six generators can cover all chromatic steps within a single octave range, an output circuit, means under the control of said secondary switches including connections between the secondary switches and the corresponding stages of all series for making pulses having frequencies oc- 22 tavely related to those of said generators drawn from the several series in accordance with the octave position of the operated switches jointly eifective in the said voutput circuit, and translating means collectively responsive to the pulses present in said output circuit capable of yproducing any combination of musical sounds required in executing conventional musical compositions.

8. A polyphonic electrical musical instrument comprising in combination a plurality of less than twelve aperiodic.frequency-dividing channels responsive to the introduction of input pulses of any desired audio frequency by the generation of `a group of output pulses having frequencies octavely related to those of the respective input pulses, a set of master pulse generators collectively capable of covering a single octave chromatic range one octave above the range of the instrument, means for selectively introducing pulses from said generators into said channels in accordance with note requirements of a musical composition, means for selectively withdrawing from said channels output pulses octavely reduced in frequencies in accordance with octave requirements of said composition, and means for rendering the withdrawn pulses collectively effective in an output circuit for translation into musical sounds.

9. An electrical musical instrument comprising in combination a series of cascaded frequencyhalving stages having aperiodic .characteristics over the audio-frequency range, a pulse generator, switching means for selectively introducing the output of said generator into any one of said stages thereby producing pulses of octavely related frequencies in the following stages, a translating means, and a connection between said translating means and one of said stages subsequent in the series to the stage into which the output of said generator is introduced to supply to said translating means output pulses for conversion into musical sound.

10. An electric musical instrument comprising in combination a series of cascaded frequencyhalving stages having aperiodic characteristics over the audio-frequency range, a pulse generator, switching means for selectively introducing the output of said generator into any one of the said stages thereby producing pulses of octavely related frequencies in the following stages, unidirectional coupling means interposed between adjoining stages to prevent the introduction of input pulses into stages preceding the input point, and translating means associated with the last stage to convert the `pulses produced therein into musical sound.

11. An electrical musical instrument comprising in combination a series of cascaded frequencyhalving stages having aperiodic characteristics over the audio-frequency range, each of said stages including a pair of space discharge tubes connected into a trigger circuit having two stable states of equilibrium, a pulse generator having a frequency adjustable within the range of one octave, switching means for selectively introducing the output of said generator into any one of the said stages thereby producing pulses octavely related to the input frequency in the following stages, and translating means associated with the last stage to convert the pulses produced therein into musical sound.

12. An electrical musical instrument comprising in combination a series of cascaded frequencyhalving stages of the triggered type having aperiodic characteristics throughout the audio- 23 frequency range, a generator operable to deliver pulses to one of said stages at a frequency adjustable in chromatic steps within a single-octave range, a set of note-deterrnining switches grouped in accordance with notes of the octave, a system of tuning elements under control of the said switches for selective connection to said generator to adjust its frequency to the corresponding note of the octave, a set of octave-determining switches grouped in accordance with octaves, said sets having corresponding pairs of switches therein arranged for joint operation, connections between tne groups of octave-determining switches and the respective Alrecluency-lfialving stages to selectively introduce the output of said generator into the stage corresponding to the octave position of the group, an output circuit, and a connection between said circuit and the last one of said stages to render the pulse energy 24 of appropriately reduced frequency present in said stage eiTective in said output circuit.

NICHOLAS LANGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,128,367 Kock Aug. 30, 1938 2,233,948 Kock Mar. 4, 1941 2,254,284 Hanert Sept. 2, 1941 2,272,070 Reeves Feb. 3, 1942 2,357,191 Hanert Aug. 29, 1944 2,403,090 Larsen July 2, 1946 2,410,156 Flory Oct. 29, 1946 2,410,883 Larsen Nov. 12, 1946 

